Photonic Interconnect and Method for Manufacturing Same

The present disclosure relates to an photonic interconnect that transmits light of an photonic interconnect on an element, and a method for manufacturing the photonic interconnect.

For high-speed and large-capacity digital communication, optical communication modules have been put into practical use in many fields instead of electrical communication modules that transmit electrical signals.

The optical communication module is required to have a function of converting an input electrical signal into an optical signal and transmitting the optical signal, and a function of receiving an optical signal from an optical fiber, restoring the optical signal to an electrical signal, and outputting the electrical signal. A light emitting element such as a light emitting diode (LED) or a vertical cavity surface emitting laser (VCSEL) is used for transmitting an optical signal, and a light receiving element such as a photo diode (PD) is used for receiving an optical signal. The light emitting element and a drive circuit are electrically connected. Similarly, the light receiving element and an amplifier circuit are electrically connected.

As technique for efficiently coupling optical fibers, photoelectric conversion elements, and the like, an optical interconnection technique for performing hybrid integration using an optical waveguide device has attracted attention.

For example, in Patent Literature 1, an photonic interconnect is formed using a thermoplastic material. In Patent Literature 1, an arch-shaped photonic interconnect connecting a first optical transmission end to a second optical transmission end in an optical circuit is formed along a shape of a silicon base body. At this time, a capillary which has a double tube structure in which a thermoplastic core material and a thermoplastic clad material are supplied from different tanks and is movable in a three-dimensional direction is used. While such a capillary is moved along the base body, the core material and the clad material are heated, injected, and solidified to perform wiring.

PTL 1: Unexamined Japanese Patent Publication No. H10-68836

In the method of PTL 1, the diameter of the photonic interconnect becomes small, and the connection strength at the connection portion between the photonic device and the photonic interconnect tends to be weak. That is, the connection is easily disconnected by a small impact or the like.

An object of the present disclosure is to suppress disconnection between an photonic interconnect and an photonic device due to vibration, impact, or the like at the time of carrying the photonic interconnect or at the time of use.

The photonic interconnect of the present disclosure is formed in an photonic device having an optical waveguide, and transmits light emitted from a optical input and output portion included in the optical waveguide. The photonic interconnect includes a connection portion connected to the optical waveguide, and a transmission line portion extending from the connection portion. The connection portion is connected to the optical waveguide while avoiding the optical input and output portion, and is wider than the transmission line portion.

An optical transmission module of the present disclosure includes the photonic device having the optical waveguide, and the photonic interconnect of the present disclosure.

A method for manufacturing the photonic interconnect of the present disclosure is a method for manufacturing the photonic interconnect that is formed in the photonic device having the optical waveguide and transmits light emitted from the optical input and output portion of the optical waveguide. The method includes a feeding step of feeding liquid resin materials while moving a material feeder, and a curing step of sequentially curing the fed resin materials to cure the resin materials in a wire shape extending in the air.

According to the photonic interconnect of the present disclosure, since the connection portion connected to the optical waveguide while avoiding the optical input and output portion has a wider width than the transmission line portion, the strength of connection is improved. This suppresses disconnection between the photonic device and the photonic interconnect due to impact or the like. According to the method for manufacturing the photonic interconnect of the present disclosure, the photonic interconnect of the present disclosure can be manufactured.

Hereinafter, exemplary embodiments will be described with reference to the drawings. The following description is illustrative and not restrictive. In addition, changes can be made as appropriate within a range in which the effects are exhibited.

1 FIG. 2 FIG. 1 FIG. 20 20 is a cross-sectional view schematically illustrating optical transmission moduleaccording to an exemplary embodiment of the present disclosure, andis a schematic plan view of optical transmission moduleas viewed from above in.

1 2 FIGS.and 20 10 15 15 12 10 As illustrated in, optical transmission moduleincludes photonic deviceand photonic interconnect. Photonic interconnectis optically connected to optical waveguideincluded in photonic device.

15 15 15 15 12 15 c d c c 1 FIG. Connection portionof photonic interconnectis wider than transmission line portionextending from the connection portion and has a drop shape. As a result, a connection area between connection portionand optical waveguideincreases, and disconnection due to impact or the like is suppressed. In the example of, connection portionhas a shape bulging with roundness also in the thickness direction.

15 18 10 12 15 c In addition, since connection portionis arranged to avoid optical input and output portionin photonic device, an adverse effect on the optical connection between optical waveguideand photonic interconnectis avoided.

These will be further described below.

10 10 Photonic deviceis, for example, a light emitting element such as a laser, a light receiving element such as a photodiode, silicon photonics (SiPh), a planar lightwave circuit (PLC), an optical fiber, or the like, and may be made of Si wafer, GaAs, or the like. In addition, photonic devicemay be, for example, a planar lightwave circuit made of a quartz glass thin film deposited on a silicon substrate.

10 11 12 11 12 12 12 12 12 11 12 12 b a b b a b Photonic deviceincludes substrateand optical waveguideprovided on substrate. Optical waveguideincludes first cladding layerand first core layerwrapped in first cladding layer. In the present exemplary embodiment, first cladding layeris formed so as to cover the upper surface of substrate. For example, first core layerhaving a diameter of 2 μm to 3 μm is formed so as to be embedded inside first cladding layer.

2 FIG. 12 12 12 12 18 12 12 a b a a As illustrated in, first core layerin optical waveguidehas a tapered shape in which the distal end is narrowed. In addition, first cladding layerin the region including the tapered shape portion is removed, and first core layeris exposed. As a result, optical input and output portionin which light leaks out of optical waveguidefrom first core layerof the tapered shape portion is configured.

12 12 11 a b 2 First core layeris formed by patterning a surface silicon layer of a silicon on insulator (SOI) substrate using, for example, a photolithography technique, an etching technique, or the like. First cladding layeris formed on substrateusing silicon oxide (SiO) as a material by using a known deposition technique such as plasma CVD, for example.

12 As the configuration of optical waveguide, in addition to the above, a semiconductor such as quartz glass, a polymer which is an organic substance, Si, silicon nitride (SiN), gallium arsenide, or indium phosphide (InP) may be used as a material.

12 18 12 10 15 a a 2 FIG. Note that, although only one first core layer(and optical input and output portionat the end of the first core layer) is illustrated in, a plurality of first core layersmay be formed in photonic device, and photonic interconnectmay be provided for each first core layer.

15 15 15 15 15 12 a b a a Next, photonic interconnectincludes second core layermade of resin through which light is transmitted and second cladding layercovering second core layer. Second core layeris preferably made of a material having high transmittance at a wavelength of light input and output by optical waveguide.

15 Photonic interconnectmay have either a step index (SI) type structure or a graded index (GI) type structure. The SI type is a type in which an interface having a clear refractive index is formed between a core layer and a clad layer, and light is propagated by reflection at the interface. In addition, the-GI type is a type in which the refractive index is the highest at the center of the core layer, the refractive index gradually decreases toward the outside, and light is guided to the center of the core layer and propagates. Here, in the GI-type, crosstalk does not occur even when the pitch between the cores is reduced. In addition, theoretically, propagation loss due to interface reflection does not occur. Therefore, a GI-type optical waveguide is desirable for an optical-electrical mixed substrate in which an optical waveguide having a high density and a long distance is required. However, the technique of the present disclosure is also applicable to the SI type.

15 15 15 12 12 15 15 15 12 15 15 c b b c d c b c d Connection portionof photonic interconnectincludes second cladding layerand is connected onto first cladding layerof optical waveguide. Connection portionhas a drop shape bulging wider than transmission line portion. Therefore, the connection area is increased, and the strength of connection between connection portionand first cladding layeris increased. Note that connection portionbulges both in width and thickness larger than the diameter of transmission line portion.

15 18 10 15 12 15 15 15 12 12 12 15 c d a a In addition, connection portionis connected while avoiding the upper part of optical input and output portionof photonic device. As a result, photonic interconnectand optical waveguideare physically connected to each other (transmission line portioncan also partially contribute to physical connection). In addition, second core layerin photonic interconnectis formed such that the distal end of the second core layer is connected to first core layerin optical waveguide. As a result, optical waveguideand photonic interconnectare optically connected to each other, and light is transmitted to each other.

15 15 12 12 15 15 15 15 12 15 15 a a c b c d As described above, second core layerthrough which light passes in photonic interconnectis connected to first core layerof optical waveguideto realize optical connection for transmitting light. In addition, connection portionformed of second cladding layerof photonic interconnectspreads in a drop shape to secure a large connection area. As a result, as compared with a case where connection portionis not provided and optical waveguideis connected by transmission line portion, the strength of the connection is improved, and it is possible to suppress a problem such as disconnection of photonic interconnectdue to an impact.

15 15 15 a b In photonic interconnect, the diameter of second core layeris, for example, about 8 μm to 9 μm, and the diameter of second cladding layeris, for example, about 120 μm.

15 Photonic interconnectcan be formed using a photocurable resin (a manufacturing method will be described later). The curing mechanism is not particularly limited to radical polymerization, cationic polymerization, or the like.

15 15 15 15 15 b a a b Examples of the material of second cladding layerof photonic interconnectinclude a bifunctional acrylate compound (for example, 2,2-bis [4-(acryloxydiethoxy) phenyl] propane), a radical generator (for example, tetra-n-butylammonium triphenyl-n-butylborate), and a photosensitizer dye reactive to an ultraviolet wavelength. In addition, examples of the material of second core layerinclude a diimmonium dye of a photosensitizer dye reactive to an infrared wavelength, and the like, in addition to the above materials. Furthermore, the resin materials for forming second core layerand second cladding layerare preferably materials whose curing is accelerated even by heat.

12 15 1 2 FIGS.and The connection form between optical waveguideand photonic interconnectis not limited to that illustrated in. Other examples of the connection form will be described below.

3 4 FIGS.and 1 2 FIGS.and 20 20 10 12 11 12 12 12 a b a. As a first modification,illustrate optical transmission moduleconstituting an edge coupler. In this example, similarly to optical transmission modulein, photonic deviceincludes optical waveguideprovided on substrate, and optical waveguideincludes first cladding layerand first core layer

12 10 12 18 a b However, in the present modification, first core layerextends to an end surface of photonic devicein a state of being wrapped in first cladding layer, and optical input and output portionis formed at the distal end portion exposed to the end surface.

15 18 15 12 10 15 c b d In addition, photonic interconnectis formed to extend from the end surface at the position of optical input and output portion. At this time, connection portionis connected to the upper surface of first cladding layerin photonic device, has a width larger than that of transmission line portion, and has a shape spreading in a drop shape. As a result, the strength of the connection is improved.

15 12 12 15 a a In addition, second core layeris connected to first core layer, and optical connection between optical waveguideand photonic interconnectis realized.

5 6 FIGS.and 1 2 FIGS.and 20 20 10 12 11 12 12 12 b b a. As a second modification,illustrate optical transmission moduleconstituting a grating coupler. Also here, similarly to optical transmission modulein, photonic deviceincludes optical waveguideprovided on substrate, and optical waveguideincludes first cladding layerand first core layer

12 12 18 a a 5 FIG. 6 FIG. In this example, a diffraction grating is provided at an end of first core layer(In, the diffraction grating is illustrated by an arrangement of black squares. In, the diffraction grating is illustrated by a fan-shaped spread portion at the end of first core layer), and optical input and output portionthrough which light leaks in the diffraction grating is configured.

15 15 15 12 18 15 18 15 d c b a c Photonic interconnectis provided with transmission line portionsuch that connection portionis connected onto first cladding layerwhile avoiding optical input and output portion, and second core layeris connected to optical input and output portion. Even in such a configuration, the strength of the connection is improved by providing connection portionhaving a shape spreading in a drop shape.

15 15 10 15 7 FIG. 1 FIG. 3 6 FIGS.to Next, a method for manufacturing photonic interconnectof the present disclosure will be described.illustrates a step of forming photonic interconnectin photonic devicecorresponding to. Note that, also in the modifications illustrated in, the method for manufacturing photonic interconnectis similar.

41 43 15 41 43 43 43 45 44 12 First, the summary is that, in the method of the present disclosure, capillary(only the tip end is illustrated) is used as a material feeder in order to feed resin materialfor forming photonic interconnect. Capillarycan discharge (feed) liquid resin materialfrom the distal end thereof while moving. As liquid resin material, a photocurable resin is used. In addition, in order to cure resin material, lighthaving the first wavelength emitted from the outside and lighthaving the second wavelength emitted from optical waveguideare used.

43 41 45 41 44 12 43 15 41 15 45 Resin materialis discharged while the distal end of capillaryis moved, and lighthaving the first wavelength is emitted while the position of the focal point is moved in conjunction with the movement of capillary. In addition, lighthaving the second wavelength is emitted through optical waveguide. Discharged resin materialsare sequentially cured, and photonic interconnectis formed according to the trajectory along which the distal end of capillarymoves. As a result, photonic interconnectcan be formed along another object, or can be formed in a wire shape extending in the air. Note that, as long as the resin is only cured in a wire shape extending in the air, the curing can be realized by using only lighthaving the first wavelength.

15 45 44 45 43 At this time, the periphery of photonic interconnectis cured by lighthaving the first wavelength, and the central portion is cured by lighthaving the second wavelength. For this purpose, for example, the intensity of lighthaving the first wavelength is adjusted so as not to supply energy enough to cure entire resin material.

15 15 15 a b As described above, photonic interconnectincluding second core layerand second cladding layerwrapping the second core layer is formed.

15 10 15 18 41 12 18 43 43 15 45 15 15 15 15 c a d c d c b. In addition, in order to more reliably fix photonic interconnectto photonic device, connection portionis formed at a position avoiding optical input and output portion. That is, the distal end of capillaryis arranged on first core layeravoiding optical input and output portion, and the discharge of resin materialis started. At this time, resin materialis discharged more than when transmission line portionis formed, and lighthaving the first wavelength is emitted. As a result, connection portionhaving a width larger than that of transmission line portionis formed. Connection portionis formed of second cladding layer

15 20 c Since connection portionhas a shape spreading in a drop shape, a large connection area is secured, and the reliability of fixing is improved. Therefore, highly reliable optical transmission moduleis realized.

Note that, in order to reliably fix the photonic interconnect, conventionally, a resin material is applied and spread on the element so as to cover the distal end of the photonic interconnect fixed in accordance with the optical input and output portion. In this case, the loss of the resin material increases. In comparison, in the method of the present disclosure, the loss of the resin material is small, and the cost is reduced.

15 41 15 15 15 15 15 44 41 10 42 15 c d c a d d After connection portionis formed, capillaryis moved so as to pass through photonic interconnect, and transmission line portionconnected to connection portionis formed. Second core layeris formed on the center side of transmission line portionby lighthaving the second wavelength. Furthermore, capillaryis moved away from the upper surface of photonic device(indicated by an arrow) to form transmission line portionwhich is a portion extending in the air.

7 FIG. 15 43 15 43 18 44 15 15 15 43 a a a a a illustrates second core layerbeing formed in resin materialbeing discharged and cured. When a part of second core layeris formed in resin materialin the vicinity of optical input and output portion, lighthaving the second wavelength is propagated by second core layer, and second core layeris further formed in a portion ahead of the second core layer. By continuing this formation, second core layercan be extended into resin materialcured in a wire shape.

43 43 41 As resin material, a mixture of an infrared curable resin and an ultraviolet curable resin is preferably used. Such resin materialis filled in a tank connected to capillary, and a controlled amount is discharged from the distal end of capillary 41.

45 43 41 15 45 15 b Lighthaving the first wavelength is focused on discharged resin materialfrom the outside and is emitted to the discharged resin material in conjunction with the movement of capillary. As a result, photonic interconnectis cured from the outer periphery and is formed in a wire shape extending in the air. Lighthaving the first wavelength mainly contributes to the formation of second cladding layer.

45 41 15 Lighthaving the first wavelength is preferably an ultraviolet laser having a wavelength of about 150 nm to 500 nm. In addition, it is preferable to use a femtosecond laser having a pulse width in femtoseconds. When the femtosecond laser is used, it is possible to cure the resin only at the tip end of capillaryin which the laser is focused and to avoid curing of the resin in the periphery thereof. Therefore, photonic interconnectcan be formed with high accuracy.

44 12 12 15 44 15 a a Lighthaving the second wavelength is emitted from first core layerof optical waveguide. As a result, the central portion of photonic interconnectis cured. Lighthaving the second wavelength mainly contributes to the formation of second core layer.

44 10 12 Lighthaving the second wavelength is preferably an infrared laser having a wavelength of about 1300 nm to 1550 nm. This may be light emitted when photonic devicesuch as the VCSEL operates, or may be light incident from an optical fiber or the like connected to optical waveguide.

45 44 15 15 After completion of photocuring by irradiation of lighthaving the first wavelength and lighthaving the second wavelength, thermal curing may be further performed as necessary. That is, temporary curing may be performed by light to form photonic interconnect, and then final curing (post-baking) may be performed by heating to complete photonic interconnect. As the post bake, for example, using a hot plate, an oven, or the like, heating is performed in a temperature range from 50° C. to 300° C. for about 1 minute to 120 minutes to complete curing (polymerization).

43 43 43 43 In the above description, it is described that the capillary that discharges resin materialfrom the distal end is used as the material feeder. However, the material feeder is not limited thereto. For example, a needle may be used. As a needle, a hollow needle with extended distal end such as an injection needle can be used. In this case, the material can be fed by discharging resin materialfrom the distal end similarly to the capillary, and curing of the resin inside can be suppressed by using a needle made of a light-shielding material such as metal. In addition, using a needle having a shape such as a cone or a cylinder that is not a hollow structure as the needle, the material can be fed in a form in which liquid resin materialspreads along the surface of the needle. In this case, it is desirable to limit the light irradiation range in order to avoid curing of resin materialin the middle of the needle.

15 Next, a sequence example of photocuring for forming photonic interconnectwill be described.

8 FIG. 43 41 18 1 45 41 43 illustrates a first sequence example. In the first sequence example, first, a resin feeding step of feeding (discharging) resin materialfrom capillaryis started. As described above, the position where discharge is started is a position avoiding optical input and output portion. Subsequently, a resin curing stepof emitting lighthaving the first wavelength while the position of the focal point is moved in conjunction with the movement of capillaryto cure discharged resin materialinto a wire shape is started.

2 44 12 15 43 a d Thereafter, a resin curing stepof emitting lighthaving the second wavelength from first core layerto cure the center side of transmission line portionis started. After an assumed amount of resin materialis fed, the resin feeding step is completed.

1 2 43 45 44 15 Thereafter, the resin curing stepand the resin curing stepare sequentially completed. In the above sequence, resin materialis cured from the outer periphery by lighthaving the first wavelength, and the uncured center side is cured by lighthaving the second wavelength. As a result, it is possible to realize GI-type photonic interconnectin which the refractive index gradually decreases from the center side toward the outside.

15 15 a b Since second core layerand second cladding layerare integrally formed, the bonding strength is high, and peeling thereof is suppressed.

9 FIG. 43 41 1 45 41 43 45 2 illustrates a second sequence example. Also in the second sequence example, first, a resin feeding step of feeding (discharging) resin materialfrom capillaryis started. Subsequently, the resin curing stepof emitting lighthaving the first wavelength while the position of the focal point is moved in conjunction with the movement of capillaryto cure discharged resin materialis started. Here, the intensity of lighthaving the first wavelength is adjusted so that the center side of a resin feeding stepbecomes uncured.

43 43 45 1 Next, after an assumed amount of resin materialis fed, the resin feeding step is completed. In addition, after the outer peripheral side of resin materialis cured into a wire shape by lighthaving the first wavelength, the resin curing stepis completed.

2 44 12 15 2 15 a d Thereafter, the resin curing stepof emitting lighthaving the second wavelength from first core layerto cure the center side of transmission line portionis started. After the center side is cured, the resin curing stepis completed. Also in this sequence, it is possible to realize GI-type photonic interconnectin which the refractive index gradually decreases from the center side toward the outside.

15 15 a b Also in this case, the bonding strength between second core layerand second cladding layeris high, and peeling thereof is suppressed.

10 FIG. 43 41 2 44 43 1 45 43 illustrates a third sequence example. Also in the third sequence example, first, a resin feeding step of feeding (discharging) resin materialfrom capillaryis started. Subsequently, in the third sequence example, first, the resin curing stepof emitting lighthaving the second wavelength to cure the center side of resin materialis started. Subsequently, the resin curing stepof emitting lighthaving the first wavelength to cure resin materialfrom the outer peripheral side is started.

43 2 1 After an assumed amount of resin materialis fed, the resin feeding step is completed. Thereafter, the resin curing stepand the resin curing stepare sequentially completed.

15 15 15 15 15 15 a b a a b In this sequence, second core layeris formed first, and then second cladding layeris formed outside second core layer. In this case, unlike the first sequence and the second sequences, SI-type photonic interconnecthaving an interface between second core layerand second cladding layeris formed.

The embodiments described above can be modified in form and details without departing from the spirit of the claims. In addition, the contents of each embodiment can be appropriately combined and replaced as long as the functions of the object of the present disclosure are not impaired.

The strength of connection of the photonic interconnect to the photonic device is improved, and the technique of the present disclosure is useful as an photonic interconnect and an optical transmission module including the photonic interconnect. In addition, the technique of the present disclosure is useful as a method for manufacturing an photonic interconnect with improved connection strength.

10 : photonic device 11 : substrate 12 : optical waveguide 12 a : first core layer 12 b : first cladding layer 15 : photonic interconnect 15 a : second core layer 15 b : second cladding layer 15 c : connection portion 15 d : transmission line portion 18 : optical input and output portion 20 : optical transmission module 20 a : optical transmission module 20 b : optical transmission module 41 : capillary (material feeder) 43 : resin material 44 : light having second wavelength 45 : light having first wavelength